The present invention is directed to an apparatus for automatically detecting the existence of a narrow band signal in the presence of wide-band noise-like interference, and finds particular use in weapons systems for recognizing a target in a clutter environment.
Autocorrelation detectors and cross-correlation detectors have been in existence for years, and most of these detectors produce an output which is proportional to the analog product of the two signals to be correlated. It is known that by first hard-limiting the two signals, a polarity coincident, or one-bit correlation, can be performed. This has the advantage of producing a normalized correlation where the output is a function of the signal-to-noise ratio, and such a correlator wherein the correlation is disclosed as being performed at zero time delay is described in the article, "Polarity Coincident Correlation Detection of a Weak Noise Source", by Helge Ekre, IEEE Trans on Information Theory, p.p. 18-23; January 1963.